JPH09113592A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved magnetic sensor having a structure capable of eliminating the disadvantage of a magnetic sensor with a compensation coil easily affected by a magnetic body and a metallic body located in the vicinity and more surely detecting the magnetic property of a magnetic body formed in a thin and long tug shape which is moved in a longitudinal direction. SOLUTION: This sensor is constructed in such a manner that an exciting coil 5 is arranged on the U-shaped magnetic core of a strong magnetic material such as ferrite or soft iron and a compensation coil 3 and a detecting coil 2 are attached to the inside of the gap 7 of the magnetic core 4. The compensation coil 3 and the detecting coil 2 are formed on an air-core bobbin 3a made of a non-magnetic material and attached in the vicinity of upper and lower sides or left and right sides. The outside of the gap 7 in which the detecting coil 2 and the compensation coil 3 are arranged is covered by a ceramic or hard resin cover.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a magnetic sensor for measuring magnetic characteristics of a magnetic material.

[0002]

2. Description of the Related Art Conventionally, there are a static magnetic field method and an alternating magnetic field method as methods for measuring the magnetic characteristics (mainly BH characteristics) of magnetic materials. In the static magnetic field method, as shown in FIG. 7A, a pair of strong magnets 21a obtained by passing a direct current from a direct current power source 22 to an exciting coil 21 are brought close to each other, and a magnetic field to be measured is generated in a magnetic field generated in a gap 21b. Place the body 24,
A magnetic flux change caused by vibrating 4 is detected and amplified by the detection coil 23 and the amplifier 25, and a detection signal is taken out (VSM system). The drawback of this method is that the apparatus is large-scaled, and therefore AC magnetic characteristics cannot be easily obtained. Next, in the AC magnetic field method, as shown in FIG. 7B, an AC current is passed from the AC power supply 26 to the exciting coil 21, the magnetic material 24 to be measured is placed in the magnetic field generated by the exciting current, and the exciting current changes. The magnetic flux density corresponding to the change in the generated magnetic field is detected and amplified by the detection coil 23 and the amplifier 25 to extract the detection signal. The device is relatively simple as compared with the previous method, but the magnetization is strong like a thin film. A special detection coil is required to measure small objects.

This AC magnetic field system includes a system without a compensation coil and a system with a compensation coil. Figure 7 (b) for the method without compensation coil
It is used to measure a relatively large magnetic material such as the core shown in FIG. 1, and the exciting coil 21 is wound around the magnetic material 24 to be measured, or the detection coil 23 is similarly measured.
The magnetic properties of the magnetic material are measured by wrapping it around No. 4. With this method, the magnetic characteristics can be measured relatively easily, but on the other hand, there is a drawback in that it takes time to wind the coil and the measured magnetic body 24 needs a large amount of mass.

In order to solve this drawback, the inventor of the present application has previously proposed Japanese Patent Application No. 7-169334 "magnetic sensor". This prior invention shows the effectiveness of the magnetic sensor with a compensation coil by the AC magnetic field method. In the magnetic sensor with a compensation coil described above, a compensation coil and a detection coil are located on both end faces of a cylindrical excitation coil. FIG. 8 shows the magnetic sensor proposed in the prior application.

[0005]

The present invention relates to an improvement of the invention of the prior application shown in FIG. 8. In this method of the prior application, the magnetic characteristics of a magnetic material having a small magnetization can be easily measured, but the excitation Magnetic lines of force generated by the coil 21 are generated from the inside of the exciting coil 21 toward the outside. This causes two problems. One of them is that if a magnetic body or a metal body is present near the magnetic sensor, the lines of magnetic force are deviated, and the generated voltage balance between the detection coil 23 and the compensation coil 27 is lost. The unbalanced state causes the voltage component of the excitation power source to become larger than the excitation voltage component of the magnetic material to be measured, which causes deterioration of the S / N ratio of the magnetic characteristic measurement. For this reason, when the magnetic sensor of the prior application is used by incorporating it into a device having a transportation system with many metal parts, it is found that there is a problem in that it is extremely difficult to use because of limitations on the mounting position and the like. When there is a metal body in the vicinity of the magnetic sensor, the magnetic field in space changes its magnetic flux density due to the polarization effect if the metal is a ferromagnetic body, and due to the eddy current accompanying a change in magnetic flux other than the ferromagnetic body. Therefore, the balance of the electromotive force with respect to the exciting magnetic fields of the compensation coil and the detection coil is disturbed by the peripheral metal body. Another problem is that when the metal conductor is present so as to surround the peripheral portion of the exciting coil 21, the magnetic field lines of the exciting coil 21 are closed as shown in the electromagnetic theory, and when a metal body crossing the magnetic field lines exists, Eddy current is generated inside the metal body, and the energy of the exciting magnetic field becomes heat or a demagnetizing field to weaken the exciting magnetic field. As a result, the magnetic substance to be measured 24 cannot be excited sufficiently, and a sufficient magnetic field cannot be applied to the magnetic substance to be measured 24, so that good magnetic characteristics cannot be obtained. Such a method of using a metal body around the sensor is common, and it has been found that there is a problem that if the magnetic sensor cannot be used with a metal body, it will be difficult to use as a limitation in use. It was

When the magnetic characteristics of the elongated tag-shaped magnetic body 24 moving in the longitudinal direction are to be detected, it is extremely difficult to detect if the easy magnetization axis of the tag is in the lateral direction. The reason is that the magnetic moment generated by the magnetic substance in the lateral direction is small and the detection signal is weak. Therefore, the exciting magnetic field must be parallel to the easy axis of magnetization. Further, since the magnetic sensor and the tag are moved in the longitudinal direction, a slight deviation in the lateral direction between the magnetic sensor and the tag conveyance system makes detection difficult with a sensor using an ordinary magnetic head with a narrow gap.

The present invention reduces the drawbacks that such a magnetic sensor with a compensation coil is easily affected by a magnetic body or a metal body in the vicinity, and the magnetic characteristics of an elongated tag-shaped magnetic body moving in the longitudinal direction. It is an object of the present invention to provide an improved magnetic sensor having a structure capable of more surely detecting

[0008]

The magnetic sensor of the present invention comprises:
A U-shaped soft iron material magnetic core having a gap, an excitation coil wound on the soft iron material of the U-shaped soft iron material magnetic core, the U-shaped soft iron material magnetic core, and the U-shaped soft iron material magnetic core In the gap, there are provided a detecting coil and a compensating coil, which are arranged side by side so that the winding axes are along the direction of the magnetic flux of the exciting magnetic field generated by the exciting current flowing through the exciting coil.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In a magnetic sensor according to the present invention, an exciting coil is arranged on a U-shaped magnetic core made of a ferromagnetic material such as ferrite or soft iron, and a compensation coil and a detecting coil are mounted in a gap of the magnetic core. It is structured.
The compensating coil and the detecting coil are formed on an air-core bobbin made of a non-magnetic material, and are vertically and horizontally mounted close to each other. The outside of the gap where the detection coil and the compensation coil are arranged is covered with a cover made of ceramic or hard resin.

FIG. 1 shows an exciting coil model, and FIG. 2 shows its magnetic field strength diagram. Reference numeral 4 denotes a magnetic core, which is formed in a U shape when viewed from the front as shown in FIG. 5 is an exciting coil,
7 is a gap. When the magnetic flux magnetic field strength of this model is calculated, the magnetic resistance Rm is

[Formula 1] Rm = 11 / μ ₀ · μ ₁ · s + 10 / μ ₀ · s (1) where, 11: magnetic core passage distance, 10: gap distance,
s: cross-sectional area of magnetic core, μ ₀ : vacuum magnetic permeability, μ ₁ : magnetic core relative magnetic permeability. However, it is assumed that there is not much spread of magnetic flux between the gaps. Further, the magnetic flux φ and the magnetic field strength H can be expressed as follows.

[Equation 2] φ = NI / Rm (2) N: Number of turns of the exciting coil 5 I: Exciting current

[Equation 3] H = φ / μ ₀ · s (3) By transforming Equation (2) and Equation (3) into Equation (1),

[Equation 4] H = NI · μ ₁ / (11 + μ ₀ · 10) ………… (4) For example, the gap distance is 10 mm, the average magnetic flux passage distance of the U-shaped magnetic core is 90 mm, and the relative magnetic permeability of the magnetic core is 1000,
When N = 300 and I = 0.3, substituting into equation (4) gives H = 9000 ampere-turns / m, and a sufficient exciting magnetic field can be obtained even with a wide gap.

[0011]

EXAMPLE FIG. 3 shows an example of a magnetic sensor according to the present invention. Reference numeral 1 is a surface cover for protection, and a non-magnetic material having abrasion resistance is used. For example, it is a ceramic material such as aluminum, or a hard plastic material such as FRP (fiber reinforced plastic) or POM (polyacetate). 2,
3 is a detection coil and a compensation coil, which are air-core bobbins 2a, 3
It has a structure in which a conductive wire is wound around a, that is, an air-core detection coil and an air-core compensation coil. Each coil has the same shape and the same number of turns, and the terminals are connected in opposite polarities to cancel the output voltage. In the embodiment shown in FIG. 3, the coils are located above and below, but they may be arranged side by side in parallel as in the example shown in FIG. Reference numeral 4 denotes a U-shaped magnetic core having a gap 7, which is made of ferrite or soft iron. An exciting coil 5 is wound around the magnetic core 4. An outer cover 6 may be a metal such as aluminum or brass as long as it is a non-magnetic material. The detection coil 2 and the compensation coil 3 are actually arranged in the gap 7, but in order to clearly show the structure of each part, in FIG.
And the compensation coil 3 are shown outside the gap 7.

In this magnetic sensor, the compensation coil 3 and the detection coil 2 are connected so as to obtain the output voltage v ₀ by adding the same number of turns and opposite winding directions, and the upper end of the U-shaped magnetic core 4 is connected. It is arranged in the gap 7. When the exciting magnetic field from the exciting coil 5 crosses the two coils 2 and 3 with the same strength, the electromotive forces excited by the coils 2 and 3 are equal and can be almost canceled on the output v ₀ side. In addition, since they are in the same plane or close to each other in the vertical direction, the loss of balance due to the change of the magnetic field due to the metal body in the vicinity is smaller than that in the conventional type positioned in polar symmetry. When the magnetic core 4 around which the exciting coil 5 is wound is formed into a U shape as shown in the drawing, the lines of magnetic force mainly pass through the gap 7 of the U-shaped magnetic core 4, and the magnetic flux spreads in the vicinity in the horizontal direction in a smaller direction than the air core type. The magnetic field strength is kept almost constant although there is a change at the magnetic core end face.

In this state, if the magnetic material to be measured 24 such as a tag is present outside the front surface cover 1 (upper part in FIG. 3),
The balance of the electromotive force due to the exciting magnetic field with respect to the detection coil 2 and the compensation coil 3 is lost, and the detection voltage v ₀ is obtained.

In this magnetic sensor, the lines of magnetic force do not spread so much in the space that it is unlikely to be affected by the magnetic or metallic body in the vicinity of the magnetic sensor. Even when detecting the magnetic characteristics of the magnetic tag 24 having the easy axis a in the short-side direction and moving in the long-side direction, the magnetic sensor of this method can generate a wide and uniform parallel magnetic field between the gaps 7. In the case of FIG. 5 which moves parallel to 7 and also in the case of FIG. 6 which moves perpendicular to the gap, it is advantageous for the positional change on the conveyance.
Since the gap in the conventional magnetic head is usually narrow, it is narrow to detect the magnetic tag 24 moving in the longitudinal direction in order to efficiently detect the magnetic characteristics of the magnetic tag 24 having the easy axis a in the lateral direction. It was extremely difficult to pass through the gap with high accuracy, and when the magnetic tag 24 was moved in a direction perpendicular to the gap with a wide width, the exciting magnetic field was perpendicular to the easy axis a. It effectively eliminates the problem that it was difficult to obtain magnetic characteristics. In the present invention, the detecting coil 2 and the compensating coil 3 are vertically or on the same plane, and the magnetic material 24 to be measured can be moved extremely close to the surface thereof. For this reason, this surface is made of ceramic,
Alternatively, it is covered with a hard resin surface cover 1.

[0015]

As described in detail above, according to the present invention, even if there is a metal body containing a magnetic substance in the vicinity, the magnetic characteristics of the magnetic substance to be detected can be reliably obtained with almost no influence. Can be detected, and is particularly effective when applied to an elongated tag-shaped magnetic body.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a model of an exciting coil used in the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the gap distance and the magnetic field strength of the exciting coil used in the present invention.

FIG. 3 is a perspective view showing the structure of the embodiment of the present invention.

FIG. 4 is a perspective view for explaining another embodiment of the present invention.

FIG. 5 is a perspective view for explaining the operation of the magnetic sensor according to the present invention.

FIG. 6 is a perspective view for explaining the operation of the magnetic sensor according to the present invention.

FIG. 7 is a connection diagram for explaining a conventional magnetic sensor.

FIG. 8 is a perspective view for explaining a magnetic sensor previously proposed by the inventor of the present application.

[Explanation of symbols]

 1 surface cover 2 detection coil 2a air-core coil 3 compensation coil 3a air-core coil 4 magnetic core 5 excitation coil 6 outer cover 7 gap 21 excitation coil 21a magnet 21b gap 22 DC power supply 23 detection coil 24 magnetic substance to be measured (tag to be detected) 25 amplifier 26 AC power supply 27 Compensation coil 28 Signal processing circuit

Claims (2)

[Claims] 1. A U-shaped soft iron material magnetic core having a gap, an exciting coil wound on the soft iron material of the U-shaped soft iron material magnetic core, and the U-shaped soft iron material magnetic core in the gap. A magnetic sensor comprising a detection coil and a compensation coil, which are arranged side by side so that the respective winding axes are aligned in the direction of the magnetic flux of the exciting magnetic field generated by the exciting current flowing through the exciting coil. 2. The detection coil and the compensation coil have a structure of an air-core detection coil and an air-core compensation coil wound on an air-core bobbin, and are arranged side by side so that respective winding axes are parallel to each other. The magnetic sensor according to claim 1, wherein: